PROJECT SUMMARY Social media use is ubiquitous among adolescents and is often used as a tool for socializing with peers. Adolescent socioemotional wellbeing is often driven by peer relationships and interactions, yet there is a paucity of research examining day-to-day social media peer interactions among adolescents. In addition, the predictors of these interactions and their prospective associations with adolescents? subjective wellbeing are understudied. Dr. Selkie is a board-certified Adolescent Medicine pediatrician whose prior research has focused on the ways social media may relate to adolescent health. This mentored career development award will allow her to learn additional methods for studying adolescent peer interactions on social media. She has built a multidisciplinary mentoring team from the University of Michigan Departments of Pediatrics, Psychology, Health Behavior and Health Education, Information, and Biostatistics as well as the University of Wisconsin Department of Pediatrics. This team will provide methodological and content expertise and guide her Training and Career Goals, which are to gain expertise and skills in: 1) theoretical models of child and adolescent social and emotional development; 2) primary data collection for research; 3) creating and testing conceptual models of peer social interaction on digital media in adolescents using principles of participatory design; 4) advanced multivariate statistical techniques including factor analysis, cluster analysis, and multinomial regression; 5) information science and social computing to inform future studies on social media behaviors in adolescents. The research plan tests a model in which childhood self-regulation predicts a social media interaction style in early adolescence, which in turn predicts a range of subjective wellbeing in the middle adolescent years. The aims are: Aim 1: Identify styles of social media peer interaction (e.g., positive (compliments, social support), neutral (planning activities, statements of fact), or negative (criticism, exclusion)) among adolescents at age 13; Aim 2: Test the hypothesis that better childhood self-regulation (higher positive emotion regulation, inhibitory control, and prosocial behavior, and lower anger, frustration, and emotional symptoms) is associated with more adaptive social media interaction styles; Aim 3: Test the hypothesis that more adaptive social media interaction styles at age 13 are associated with greater subjective wellbeing (i.e., higher self-esteem, social connectedness with classmates and close friends, and positive affect and lower loneliness, negative affect, and perceived stress) at ages 15-16. These Aims will be carried out through direct observation of social media behavior in a cohort of 150 low-income adolescents, followed by analysis of associations between these behaviors, previously collected data on child self-regulation, and data on subjective wellbeing in later adolescence. This award will provide Dr. Selkie with the training and experience to become an independent investigator and develop future R01 grant applications.